Friend
You are taking a chance with that type of replacement. The KT88 has different bias points as well as different filament requirements. See links below to compare:
http://tdsl.duncanamps.com/show.php?des=KT88
http://tdsl.duncanamps.com/show.php?des=6L6
Also, when a tube is not biased properly - it is not happy. Therefore, it most likely will not be imporessive as it is not being utilized properly. One last thought - different tubes work best with certain input and driver tubes.
You are taking a chance with that type of replacement. The KT88 has different bias points as well as different filament requirements. See links below to compare:
http://tdsl.duncanamps.com/show.php?des=KT88
http://tdsl.duncanamps.com/show.php?des=6L6
Also, when a tube is not biased properly - it is not happy. Therefore, it most likely will not be imporessive as it is not being utilized properly. One last thought - different tubes work best with certain input and driver tubes.